This invention relates to an integral device for forming and metering a mixture of air and fuel in an internal combustion engine of the type comprising a plurality of fuel injectors operated and controlled by a central electronic unit.
Devices of this type normally comprise an air manifold connected to the air filter by a duct the passage of which is controlled by a throttle valve, and a plurality of ducts for feeding air from said manifold to the combustion chamber of each engine cylinder. Each fuel injector is positioned along one of said ducts immediately upstream of the combustion chamber, and the fuel is fed to the injector through a pipe forming part of a fuel feed circuit, the fuel being fed into the circuit by an electrically driven pump at a predetermined pressure controlled by a suitable pressure controller.
The device also comprises a further duct which connects the region downstream of the air filter to said manifold and is controlled by a suitable valve to feed predetermined air quantities during engine cold starting, when the main duct controlled by the said throttle valve is almost completely closed by the valve. Devices of the aforesaid type have certain drawbacks.
Firstly they comprise completely separate components fixed in various ways to the engine or to the vehicle body and connected together by a large number of pipe portions to form the main feed air circuit, the cold start secondary air circuit and the fuel circuit.
Consequently such devices are of large overall size, require a large number of complicated operations for assembly, and are of poor reliability because of the ease with which said pipes provided between the various device components can separate or break.
Furthermore the operation of such devices is not optimised for basic engine operating conditions because of the constant volume of the air pipes which connect the various components together, and because of the high hydrodynamic resistance. In addition in certain applications, because of the presence of vapour in the petrol circuits there are hot start difficulties after stoppage.